JRGK Earthquakes

EarthquakesEarth Science Unit 12

Why & HowSo…why do earthquakes happen?Tectonic plates are always movingThe boundary between 2 tectonic plates is called a fault

Faults are areas where earthquakes happen…how?

Why & HowThe rocks on each side of the fault are moving slowly.

As they move, sometimes they get stuck. If they stay stuck for a while, a lot of pressure builds up.

When the rocks finally get un-stuck they break (fracture) and move again, and the rocks “rebound” past the place where they were stuck and keep moving slowly past each other.

This is the Elastic Rebound Theory

Mechanics of an Earthquake

Where the plates actually get stuck is where the earthquake begins…called the focus.

The point on Earth’s surface directly above the focus is the epicenter.

Which plate boundary would have deeper focus earthquakes?

Seismic Gaps

Sometimes the plates get stuck for a long time

Why could this be bad?We identify these places because they haven’t released any seismic waves in a long time.

This is a “gap” in the record of seismic activity

What makes an Earthquake Dangerous?So, plates get stuck and then move quickly…what does this really do?

This creates vibrations (waves) that travel through the ground.

What does a wave look like?

Seismic WavesThere are 4 types of seismic waves released in an earthquake.

The first two move deep within the Earth, and are called Body Waves

The second two move through the surface of the Earth and are called Surface Waves

Wave Time in Earthquake

Describe Movement

Use Arrows to Describe Movement

Amount of Damage Caused

P Wave        

S Wave        

Love Wave

Rayleigh Wave

Seismic Waves

WhereWhat kinds of plate boundaries usually create earthquakes?

Quick Quiz #1The place underground where an earthquake actually begins.

The seismic wave that arrives first in an earthquake

Love and Rayleigh waves are the two types of ____________ waves.

Why is a seismic gap dangerous?

WhereWhat kinds of plate boundaries can create earthquakes?

ANY kind of plate boundary!Boundaries are places where tectonic plates rub against each other.

How are their earthquakes different?

Transform Boundary EarthquakesForm where the plates move past one anotherUsually begin near the surface…why?Create lots of vibrations near the surface, which cause a lot of damage

Largest in the world is along the coast of California

Convergent Boundary EarthquakesWhere one plate subducts beneath another plateUsually begin deep underground…why?Their vibrations are felt over a large areaIf they are totally underwater, they form:

Underwater volcanoes, which can make island arcsTsunamisExample: Aleutian Islands

If they are on land, they form:Terrestrial volcanoesExample: West coast of South America

Underwater Convergent Boundary

Aleutian Islands, Alaska

Terrestrial Convergent Boundary

Terrestrial Convergent BoundaryAndes Mountains, South America

The Pacific Ring of Fire

One of 3 major earthquake zones in the world

Surrounds the Pacific Ocean

Contains Transform & Convergent boundaries.

The Eurasian-Melanesian Mountain

BeltOne of the 3 major earthquake zones in the worldMountains that extend from Europe into AsiaContains mostly Convergent Boundaries

Divergent Boundary Earthquakes

Form where the plates spread apart

Usually begin near the surface

Usually too small to be felt by people

Most found on the Ocean Floor

The Mid-Atlantic Ridge

One of 3 major earthquake zones in the worldSplits the Atlantic OceanMostly underwater

Magnitudes of EarthquakesThe Richter Scale: Measures Energy ReleasedMeasures from 1-12, with 1 being the smallest and

12 being the highest.Major Earthquake: over 7 Moderate Earthquake: 6-7Minor Earthquake: 2.5-6Microquake: less than 2.5 (cannot be felt by

people)

The Mercalli ScaleMeasures in Roman numerals from 1-12 (I – XII)

The Richter Scale

The Richter Scale

Mercalli Scale

Magnitudes of EarthquakesThe largest earthquake ever recorded was estimated at 9.6 on the Richter scale, and caused massive damage. It is the only earthquake ever recorded over 9.

Most major earthquakes are between 7 and 8, and most scientists believe only 1 or 2 earthquakes over 8 will happen in 100 years.

Most scientists do not believe that an earthquake larger than 10 on the Richter Scale could ever happen.

On the Richter Scale, the highest number (12) is described as “total destruction of the Earth, where the Earth would be split in two.

Finding Epicenter & Magnitude

http://www.sciencecourseware.org/virtualearthquake/VQuakeExecute.html

Quick Quiz #2The deepest earthquakes are found at ________________ boundaries.

The west coast of North America is part of an earthquake zone known as the ___________________.

To find the epicenter of an earthquake, you need to know the arrival time of the ______ wave from 3 recording stations.

A ________________ earthquake has a Richter magnitude between 6 & 7.